1. Field of the Invention
The present invention relates to an air breather system for preventing blowback at fueling etc. in the fuel tank of a vehicle.
2. Description of the Prior Art
As shown in FIG. 3, when fuel is to be fed into the fuel tank of a vehicle, a filler gun 1 is put into the mouth of a filler pipe 3 for introducing the fuel into the fuel tank. The front end of the filler gun 1 is fitted through a mechanical seal 5 which is disposed in the mouth of the filler pipe 3. Then, the vicinity of the front end of the filler gun 1 comes to have a negative pressure under the influence of the inflow of the fuel into the filler pipe 3 with the fuel feed. On account of the negative pressure, the fuel shuts up the auto-stopping hole of the filler gun 1, to incur a malfunction in which the filler gun 1 is automatically stopped notwithstanding that the tank is not filled u with the fuel. In order to prevent the malfunction, a slender air breather pipe 7 which bypasses the mechanical seal 5 has heretofore been provided in the filler pipe 3 as shown in FIG. 3. Thus, the negative pressure region near the front end of the filler gun 1 is supplied with the atmospheric air from the mouth of the filler pipe 3.
According to the prior-art technique stated above, the malfunction of the automatic stop of the filler gun 1 is preventable. However, when the fuel tank has become full, it temporarily exhibits a positive (plus) internal pressure in case of the proper automatic stopping of the filler gun 1 based on the closure of a liquid level regulating float valve with which the fuel tank is furnished. Consequently, the vapor 9 of the fuel is emitted to the atmosphere through the air breather pipe 7. This might result in a situation where the fuel itself flows out in mixing with the vapor 9.
Further, when the fuel is being fed at a low flow rate by the use of the filler gun 1, the vapor is sometimes emitted to the atmosphere through the mouth of the filler pipe 3 by the backward flow thereof. More specifically, the quantity of that air in the fuel tank which is imbibed through the auto-stopping hole of the filler gun 1 is proportional to the quantity of fueling. Accordingly, when the quantity of fueling per unit time is small, also the quantity of the imbibed air naturally becomes small. On the other hand, the fuel under feed flows into the tank while swirling and undulating within the filler pipe 3, and the vapor 9 is produced in large amounts within the filler pipe 3 at that time. When the quantity of the vapor 9 exceeds the allowable quantity of the air inhibition, the vapor 9 flows backward through the air breather pipe 7 and is emitted to the atmosphere through the mouth of the filler pipe 3.